1. Field of the Invention
The present invention relates to a rotary powder compression molding machine that compresses a powder material to mold a tablet, food, an electronic component, or the like.
2. Description of the Related Art
Conventionally, in a rotary powder compression molding machine that compresses a powder material to mold tablets, for example, irregular tablets may be produced in some cases due to abnormal pressure in molding. Because such tablets cannot be treated as products, the tablets must be excluded from products. Therefore, a defective article eliminating device is mounted in the rotary powder compression molding machine. For example, there is a rotary powder compression molding machine as described in International Publication No. WO 2008/038070 in which a control valve is opened in response to a signal output from a control unit and air from a compressed air source is injected from a discharge nozzle via the control valve to eliminate the defective molded article.
In this rotary powder compression molding machine, a pressure gage is provided in a feed path between the compressed air source and the control valve so as to detect a failure of the control valve. Static pressure in the feed path is monitored based on an electric signal output from the pressure gage and a control unit outputs an error signal when the static pressure is lower than the minimum pressure set in advance.
In general, if the compression air is not injected from the discharge nozzle for some reason in the rotary powder compression molding machine, the defective article is not eliminated and collected together with conforming articles. For example, if the control valve fails, the compressed air is not injected from the discharge nozzle and the defective article is not eliminated. Therefore, the defective article may be mixed into the conforming articles and all the collected conforming articles may not be used as products because of the only one defective article in some cases.
In order to solve the problem described above, the machine in International Publication No. WO 2008/038070 measures pressure of the compressed air in a feed line connected to the discharge nozzle to verify whether or not the compressed air is injected from the discharge nozzle. In particular, if the pressure is low as a result of the measurement of the pressure in the feed line, it indicates that the control valve is open. If the pressure is high, it indicates that the control valve is closed or the discharge nozzle is clogged. In this way, whether or not the compressed air is injected is verified.
However, though it is possible to verify that the compressed air is injected from the discharge nozzle, it is impossible to verify whether or not a path of a target molded article has actually been changed or whether or not the target molded article has been retrieved.
Moreover, though International Publication No. WO 2008/038070 mentions taking out of a sample, it is impossible to verify whether or not the target sample has actually been retrieved for the same reason as the above.